Liquid heat transfer of naphtha feed to a reforming zone



l. V. DE CHELLIS May 17, 1960 LIQUID HEAT TRANSFER OF NAPHTHA FEED TO A REFORMING ZONE Filed July 26, 1957 2 Sheets-Sheet 1 moo 9. .32 555m a EEMV M ozEoQkI m r m *m min- 6 wow mm mm. Nm 25w mm B Y 9 2 mD I: Q 1/ 2 1 om m mi R 2) Qv mm mm 835%.". mm mm mm 000 2 3 N I 33552503 ll og- \J m ll 8:28am 3:30 8 on mm May 17, 1960 v. DE CHELLIS LIQUID HEAT TRANSFER OF NAPHTHA FEED TO A REFORMING ZONE 2 Sheets-Sheet 2 Filed July 26, 195? osmwmuo B 5 f m.

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o mm. 358,61 mm. my my B om vom: y 39 m moo 238m 1 u 8E8 29? mm. moo m wQ m \wn 3 5% 2 30 1283mm mm. m9 2. NB wow 3. my pE o I 35mm Q Itulo V. DeC llis AGENT United States Patent LIQUID HEAT TRANSFER OF NAPHTHA FEED TO A REFORMING ZONE Italo V. De Chellis, Woodbury, NJ., assignor to Socony Mobil Oil Company, Inc., a corporation of New York The present invention relates to the deposition of insulating deposits laid down on 'metal heat transfer surfaces in contact with unstable petroleum fractions such as naphtha, and, more particularly, to means for heating unstable naphtha to processing temperatures without the formation of prohibitive depositions in heat exchanger tubes and the like.

With the advent of reforming to produce gasolines of increased octane rating from-naphthas and gasolines of lower octane rating than that required for modern high compression, spark-ignited, internal combustion engines, the problem of tube fouling in heat exchangers and furnaces has come to the fore. It has been found that petroleum fractions which deposit no sediment at ambient temperatures precipitatedeposits of unknown composition on tube surfaces when heated to temperatures of 350 to 1200 F. in heat exchanges and furnaces} These deposits are of such magnitude that designed on-stream periods of, for example, 180 days are reduced to as little as 30 to 90 days. The nature of the deposit varies with the nature of the fuel and does not appear to be correlated with the con centration of a particular type of material but results from a number of factors among which are they olefin, diolefin, nitrogen, sulfur and oxygen content of the petroleum fraction.

Patented May 17, 1950 ice ' 2 ture. Therefore, in standard evaluation these two (pressure and rate of flow) were held constant to facilitate better control and reproducibility of results.

An unstable naphtha is one which when subjected to the foregoing Tube-Wall Deposit Test deposits more than about 3.5 to about 35 milligrams of material per liter of naphtha.

The present invention provides a method of raising the temperature of an unstable naphtha as determined by the foregoing test to aprocessing temperature above about 350 'F. by mixing the unstable naphtha with a heat carrier comprising a liquid petroleum fraction having a sufficiently different boiling range that the heat carrier is readily separated from the heated naphtha, Suitable heat carriers are petroleum fractions boiling above about 500 F. The heat carrier is a petroleum fraction stable under the conditions of the aforedescribed Tube wall deposit test, i.e., a petroleum fraction which deposits not more than about 0 to 3 milligrams of material per liter of fraction in the Tube wall deposit test. The heat carrier is heated to at least the temperature at which the unstable naphtha is to be processed and mixed with the unstable naphtha in an amount such that when the heated unstable naphtha is separated from the heat car-' rier the temperature of the heated unstable naphtha is suitable for the reaction to which it is to be subjected. Thus, for example, when treating an unstable naphtha to remove contaminants such as organic sulfur and/or organic nitrogen compounds processing temperatures of about 600 to about 800 F. are employed. In accord 'ance with the principles of the present invention a heat carrier such as gas oil boiling above about 500 F. 'is heated to about 800 to about'2000 F; and mixed with the'unstable naphtha in' the ratio of about 10.0 to about 0.5 barrel of gas oil per barrel of unstable naphtha. After the unstable naphtha has been heated to the re quiredreaction temperature the heated unstable naphtha For evaluating various methods of treating petroleum Tube-wall deposit test The instrument consists'of an internally heated stainless steel tube having an inside diameter of inch, an

is separated in any suitable manner from the heat carrier and introduced into the reaction zone, in this instance a hydrodecontamination zone at reaction temperature. The separated heat carrier'is recycled to the carrier heat-j ing unit or further processed in whole, or in part.

' The present invention will be readily understood by those skilled in the art after reading the following descriptioninconjunctionwith the drawings in which 1 Figure 1.is.a highly diagrammatic flowsheet illustrating the principles of the present invention in which unr stable naphtha is heated to hydrodecontarninating temoutside diameter of /2 inch and a length of 17% inches.

A selected amount of the petroleum fraction to be tested is passed at a pressure of 150 p.s.i.g. over the internally'heated tube at a selected flow rate suchthat the petroleum fraction is heated to 500 F. during passage over the internally heatedtube. The' tubeis weighed before and after contact with the selected amount of petroleum fraction being tested. The difierence between the weight before and after is a measure of the onstream timewhich heat transfer surfaces in contact with peratures of at least 600; F. by admixture with stable gas oil wherein the stable gas oil'is recycled or in part or all further processed; and v Figure 2 is a highly diagrammatic flowsheet illustrating the principles of the present invention in which the heat carrier is a heatedcatalytic cracking recycle stock with which the unstable naphtha is mixed, the mixture sub jected to hydrocracking, the original naphtha and the naphtha produced during hydrocracking reformed, and the hydrocr'acked products boiling above the end point of gasoline returned to the catalytic cracking process.

' In Figure 1 amethod of heating unstable naphtha is illustrated in which an'unstable light naphtha is drawn from asourcenot shown through pipe 1 by pump 2 and discharged at a pressure higher than thepresure in the hydrodecontaminator into pipe 3. The unstable naphtha.

1 flows through pipe 3 to absorber 4. Unstable heavy naphthe is drawn from a source not shown by pump 5 through pipe 6 and discharged into pipe 7 at a pressure higher than In absorber 4 the unstable naphthas contact the gas in excess of that required for hydrodecontamination and extract light hydrocarbons from the gas. The gas contains hydrogen, hydrogen derivatives of contaminants present in the naphtha and C to C hydrocarbons. The hydrogen-containing .gas flows from liquid-gas separator 8 and from stripper ,9 through conduits 10. and :11 respectively. The enrichedunstable .light andheavy naphthas arc ,drawnfromabsorber 4 through pipe12 by pump .13.

Stable heat carrier, e.g., gas oil is drawn from a source not shown through pipes 14 andlS by pump 16 and discharged at a pressure higher than that of the hydrodecontaminator into pipe 18. The heat carrier flows through pipe 18 to coil 19 in carrier furnace or heater 20 where the heat carrier (gas oil) is heated .to a temperatureisuch that when mixed with the unstable naphthas in the ratio of 0.5.10.0 barrels of gas oil per barrel of unstable naphthas the temperatureof the mixture is thatof hydrodecontamination. Thus, for example, when. the temperature required in the hydrodecontamination reactor 21 is 700 F. the heat carrier, e.g., gas oil, is heated to about 800 to about 1600 F. and mixed with the unstable naphtha-s in the ratio of about 10.0 to about 0.5 barrels of gas oil per barrel of naphthas. When desirable a small amount, e.g., about 50 to about. 500 s.c.f./ barrel of gas such as hydrogen-containing recycle gas from a reformer is introducedinto pipe 18 through pipe 25 to reduce the tendency of the gas oil to coke the heater tubes. 7

Theheated heat carrier, e.g., gas oil, flows from coil 19 in heater 2.0 through pipe 22. Pump '13 discharges enriched unstable naphtha into pipe 23. The unstable naphtha flows through pipe 23 into pipe 22 where the unstable naphtha mixes with the heated heat carrier, e.g., gas oil. The mixture of heat carrier and unstable naphtha flows through pipe 22 to a separator 24 such as a flash drum or other separator suitable for separating naphtha from heat carrier.

.In separator 24 the heated unstable naphtha separates from .the stable heatcarrier. The choice of separator is dependent upon the temperature difference between the endpoint of the unstable naphtha and the initial boiling point of the heat carrier. The greater the aforesaid temperature difference the simpler the separator. The heated unstable naphtha (and any hydrogen introduced upstream of the carrier furnace) flows from separator 24 through .pipe 26 to pipe 27. The separated heat carrier .flows from separator 24 throughpipes 2.8 and to the'suction side of pump 16. When desirable or necessary a portion of the recycled heat carrier, e.g., gas oil, is diverted through pipe .47 to furtherprocessing such as catalytic cracking, hydrocracking, hydrofinishing, and the like.

Any fouling matter or polymers formed during the heating of the unstable naphtha remains suspended in the heat carrier and when the heat carrier is separated from the heated naphtha the high molecular weight fouling material and/ or polymers how with the heat carrier.

The separated heated naphtha flows from separator 24 through pipes 26 and 27 to the processing step for which it was necessary to raise the temperature of the unstable naphtha above 380 F. In the illustration the processing step is hydrodecontamination.

Hydrodeccntamination, for the purpose of the illustralion, takes place in the presence of hydrogen and a hydrogenating catalyst such as a mixture. of. oxides of cobalt and molybdenum on a carrier such asalumina at temperatures of about 600 to about 800 F. at pressures of about 150 to about 2000 p.s.i.g. in the presence of about 500 to about 2000 s.c.f. (standard cubic feet) of hydrogen per barrel of naphtha. The necessary hydrogen flows to pipe 27 from stripper 9 through pipe 11 and is mixed with the heated unstable naphtha in pipe 27. When desirable or necessary hydrogen from an extraneous source, such as reformer recycle gas, flowing through pipes 29 seamen and 30 supplies all or a part of the hydrogen reguired in hydrodecontaminating reactor 21.

The reaction products and recycle gas flow from bydrodecontaminating reactor 21 through pipe 31 to heat exchanger 32 Where the reactor effluent is in indirect heat exchange relation with the bottoms of stripper 9 flowing from stripper 9 through pipe 33, heat exchanger 34, and pipe 35 to heat exchanger 32 and thence through pipe 36 to further processing, e.g., reforming.

The efiluent from the hydrodecontaminating reactor 21 flows from heatexchanger 32 through pipe 37 to condenser 38 where the effluent is cooled to a temperature such that at the pressure existing C hydrocarbons condense. From condenser 38 the condensed and uncondensed hydrodecontaminating reactor efiluent flows through pipe 39 to liquid-gas separator 8.

In liquid-gas separator 8 the condensed effluent separates from the uncondensed effluent. The uncondensed efiiuent flows from liquid-gas separator 8 through pipe 10 to absorber 4 as previously described herein. The condensed effluent together with dissolved or entrained gases and hydrocarbons lighter than C flows through pipe 40 to the suction side of pump 41. .Pump 41 .discharges the condensed efliluent into pipe 42 through which the condensed efiluent flows to heat exchanger 34 Where i the condensed effluent is in indirect heat exchange relation with the bottoms of stripper 9. vSince the condensed efiluent is unstable naphtha which has been heated to temperatures above 350 F. and contacted with a hydrogenating catalyst under conditions which convert precursors of or deposit forming constituents of .the unstable naphtha, the condensed efliuent does not tend to form.

troublesome deposits in heat exchanger 34.

The heat exchanged condensed efiluent flows .from heat exchanger 34 through pipe 43 to stripper 9. When necessary the temperatureof the condensed efiluent is raised to that necessary to strip hydrogen sulfide, ammonia and other volatile hydrogen derivati es of contaminants present originally in the unstable naphtha, e.-g., arsine, from the condensed efiluent in heat exchanger 44. .A temperature of about 300 F. is usually sufficient. The heated condensed efliuent flows from heat exchanger 44 through pipe 45 to stripper 9. To assist .in stripping the condensed eflluent hydrogen from an extraneous source, e.g., reformer recycle gas flowing from conduit 29 through conduit 46 is introduced into stripper 9.

Hydrogen, residual hydrogen derivatives of contaminants originally present in the unstable naphthas and bydrocarbons lighter than C; flow from stripper 9 through pipe 11 to absorber 4. All of the overhead from stripper 9 or a part thereof is diverted from pipe 11 to pipe 27 to provide a part of all of the hydrogen required in hydrodecontaminating reactor 21.

The bottoms of stripper 9 is the C fraction of the condensed efiluent hydrodecontaminated to provide a naphtha suitable for reforming over a reforming catalyst, e.g., a platinum-type reforming catalyst. The bottoms flow from stripper 9 through pipe 33, heat exchanger 34, :pipe 35, heat exchanger 32 and pipe 36 to the reforming unit.

Illustrativeof another application of the principles of the present invention is the use of a petroleum fraction to be processed as a heat carrier. Thus, for example, as disclosed in the copending application for United States Letters Patent filed in the names of K. M. Elliott, E. A. Schraishuhn and P. R. Walton, heavy recycle stock from a catalytic cracking process can advantageously be hydrocracked before being subjected to catalytic cracking. Such heavy recycle stock is a satisfactory heat carrier for the purposes of the present invention. The use of such a catalytic cracking recycle stock as a heat carnier is illustrated in Figure 2. Thus, heavy recycle stock flows from a source not shown through pipe 101 to the suction. side of pump 102. .Pump 102 discharges at above hydrocrack'ing pressure into pipe 103. The heavy fwycle sto ws t o hnip 1 3 t tha sr z 104 where the heavy recycle stock is in indirect heat exchange relation with the overhead from separator 105 flowing through pipe 106 to the suction sideof pump 107. Pump 107 discharges into pipe 108 through which the overhead from separator 105 flows to heat exchanger 104. 1

vFrom heat exchanger 104 the heated heavy recycle stock flows through pipe 109 to heat carrier furnace or heater 110. Downstream from furnace 110'it is'preferred to mix a small amount, say about 50 to about 500 s.c.f./ b. of gas with the heavy recycle stock. Reformer recycle gas is suitable for this purpose and is introduced from a reformer not shown into pipe 109 through pipe 111. The heavy recycle stock is heated in the coil 112 in furnace 110 to a temperature sufiiciently above hydrocracking temperatures that when the heated heavy recycle stock is mixed with unstable naphtha in the ratio of about 5.0 to about 1.0 barrels of heavy recycle stock per barrel of unstable naphtha the resulting mixture has a temperature suitable for hydrocracking. In general, the heavy recycle stock is heated to a temperature of about 850 F. to about 2000 F. Unstable naphtha as defined hereinbefore flows from a source not shown through pipe 139 to the suction side of pump 140. Pump 140 discharges the unstable naphtha into pipe 113- at at least the pressure in hydrocracking reactor. The unstable naphtha flows through pipe 113 to pipe 115. The heated heavy recycle stock flows from coil 112 through pipe 114 to pipe 115. In pipe 115 the unstable naphtha and heated heavy recycle stock mix and flow to pipe 116 Where the mixture of heavy recycle stock and unstable naphtha at a temperature of about 800 to about 1000 F. and a pressure of about 1000 to about 5000 p.s.i.g. is mixed with hydrogen containing gas flowing from pump 117 as described hereinafter. The mixture of heavy recycle stock and unstable naphtha is mixed with hydrogencontaining gas in the mol ratio of about 10 to about 50 mols hydrogen per barrel of mixture. The amount of hydrogen circulation required usually is about 1000 to about 20,000 s.c.f. per barrel of mixture.

In hydrocracker 118 the mixture of heavy recycle stock and unstable naphtha is contacted in the presence of hydrogen with a particle-form catalyst having hydrogenating and cracking capabilities. At the present time it is preferred to use a mixture of oxides of cobalt and molybdenum on a carrier such as alumina. The reaction products, i.e., reactor eflluent comprising unstable naphtha, hydrocracked naphtha, hydrogen, hydrogen derivatives of organic sulfur compounds and organic nitrogen compounds, for example, hydrogen and C and heavier hydrocarbons together with the heavy recycle stock which has not been converted to lighter hydrocarbons flow from hydrocracker 118 through pipe 119 to separator 105.

Separator 105 is of any suitable type capable of separating naphtha and lighter hydrocarbons from heavy recycle stock. A flash drum gives satisfactory separation. Separator 105 operates at a temperature such that at the existing pressure the unconverted heavy recycle stock is in the liquid phase. At pressures above 500 p.s.i.g. the heavy recycle stock is liquid at temperatures below about 850 F. The heavy recycle stock flows from separator 105 through pipe 139. The naphtha (original and hydrocracked naphtha) together with lighter hydrocarbons, hydrogen, and volatile hydrogen derivatives of the contaminants present in the charge to separator effiuent flow from separator105 through-com duit 106 to. pump 107. From pump 107 the uncondensed separator eflluent flows through conduit 108 to heat exchanger 104 where it is in indirect heat exchange relation with heavy recycle stock as described hereinbefore. From heat exchanger 104 the uucondcnw sepdensed separator efiluent flows through pipe'124 to the suction side of pump 125.

Pump 125 discharges the C and heavier hydrocarbons, etc., into pipe 126 through which the C and heavier hydrocarbons, etc., flow to heat exchanger 127. In heat exchanger 127 the C and heavier hydrocarbons, etc., are in indirect heat exchange with the bottoms of stripper 128 flowing through pipe 129. The heated C; and heavier hydrocarbons, etc., flow from heat exchanger 127 through pipe 130 to stripper 128. When necessary the temperature of the contents of pipe 130 can be raised to the temperature necessary to volatilize substantially all oftheconstituents thereof lower boilingthan C hydrocarbons.

In stripper 128 the hydrocarbons boiling below the boiling point of C hydrocarbons togetherwith residual amounts of other volatile components of the contents of pipe 130 are taken as overhead. When the hydrocrackeris operated under relatively mild conditions substantially all of the overhead flows through pipe 131 to pipe 123 and thence to the suction side of pump 117. When necessary hydrogen-rich gas such as reformer re cycle gas flows from a source not shown through con duit 132 to conduit 123 to supply hydrogen for the hydrocracking reaction. To assist in stripping the C and heav ier hydrocarbons, etc., in stripper 128 it is'preferred to 'the hydrocracker hereinafter designated uncondensed.

naphtha now stabilized and any naphtha produced in the hydrocracker from the heavy recycle stock. The major portion of the bottoms flows from stripper 128 through pipe 129 to heat exchanger 127 and thence through pipe 135 tothe reforming unit.

A minor portion of the bottoms of stripper 128 flows through a reboiler comprising pipe 136 to heat exchanger 137 and thence through pipe 138 back to stripper 128.

I claim:

1. A method for reacting an unstable naphtha which forms deposits of low heat conductivity upon heat exchange surfaces at temperatures above about 350 P. which comprises mixing said unstable naphtha at a temperature below about 350 F. with a relatively stable hydrocarbon liquid heat-carrier having a distillation range at least 50. F. above that of said naphtha the said heat carrier being at a temperature and in an amount sufiicient to raise the temperature of said mixture above 350 F. and at least to the predetermined temperature for reac-- tion of the aforesaid naphtha, separating the thus-heated naphtha from said heat-carrier, and subjecting said heated naphtha to the aforesaid reaction.

2. The method as set forth and described in claim 1 wherein the heat carrier is gas oil.

3. The method as set forth and described in claim 1 wherein the heat carrier is gas oil and at least a portion of the "separated heat carrier is subjected to further processing.

"4."The method as set forth and described in claim 1 wherein the'heat carrier is catalytic crackin recycle stock and wherein prior to separating the naphtha from the heat carrier the mixture of naphtha and heat carrier is subjected to hydrocracking conditions.

5. The method as set forth and described in claim 1 wherein the heat carrier is catalytic cracking recycle stock, wherein prior to separating the naphtha from the heat carrier the mixture of naphtha and heat carrier is subjected to hydrocracking conditions, and wherein the separated heat carrier is subjected to catalytic cracking.

' References Cited in the lfile at this patent NITED STATES PATENTS Dinning Sept. 26, 1944 Schulze July 31, 1945 Friedman Jan. 25, 1955 Hannah June 21, 1955 Bushnell et al Nov. 27, 1956 Keith Jan. 29, 1957 Home et al July 30, 1957 

1. A METHOD FOR REACTING AN UNSTABLE NAPHTHA WHICH FORMS DEPOSITS OF LOW HEAT CONDUCTIVITY UPON HEAT EXCHANGE SURFACES AT TEMPERATURES ABOVE ABOUT 350*F. WHICH COMPRISES MIXING SAID UNSTABLE MAPHTHA AT A TEMPERATURE BELOW ABOUT 350*F. WITH A RELATIVELY STABLE HYDROCARBON LIQUID HEAT-CARRIER HAVING A DISTILLATION RANGE AT LEAST 50*F. ABOVE THAT OF SAID NAPHTHA THE SAID HEAT CARRIER BEING AT A TEMPERATURE AND IN AN AMOUNT SUFFICIENT TO RAISE THE TEMPERATURE OF SAID MIXTURE ABOVE 350*F. AND AT LEAST TO THE PREDETERMINED TEMPERATURE FOR REACTION OF THE AFORESAID NAPHTHA, SEPARATING THE THUS-HEATED NAPHTHA FROM SAID HEAT-CARRIER, AND SUBJECTING SAID HEATED NAPHTHA TO THE AFORESAID REACTION. 